Telephone system.



' No. 718,215. PATENTED JAN.1s,19os.

I. H. PARSONS & T. SLOPER.

TELEPHONE SYSTEM.

APPLICATION FILED FEB. 28, 1902.

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PATENTED JAN. 13, 1903 I. H. PARSONS & .T. SLOPER.

TELEPHONE SYSTEM.

APPLICATION FILED FEB. 28, 1902. N0 MODEL.

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TELEPHONE SYSTEM.

APPLICATION FILED, 173.28, .1902.

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N0 MODEL.

STATES ATENT OFFICE.

ISAAC HARDY PARSONS, OF LEICESTER, AND THOMAS SLOPER, OF DEVIZES, ENGLAND.

TELEPHONE SYSTEM.

SPECIFICATION forming part of Letters Patent No. 718,215, dated January 13, 1903.

Application filed February 28,1902. Serial No. 96,138. (No model.)

To all whom it may concern:

Be it known that we, ISAAC HARDY PAR- soNs, of the firm of Gent & 00., residing at Faraday Works, Leicester, and THOMAS SLO- PER, residing at 14 Brittox, Devizes, Wilts,

England, subjects of the King of Great Britain, have invented new and useful Improvements in or Connected with Telephone Systems, of which the following is a specification.

Our invention relates to telephone systems of the kind wherein the instruments at each station or point from which communication is to be made are connected by an independent wire having branches extending to a :5 switchboard in connection with the instruments at all or some of the other stations which it is desired to place in communication. In systems of this class it is sometimes possible for a person at a station which is not in direct circuit with another station to overhear a conversation which is proceeding between two connected stations. Various attempts have been made to prevent conversation from being thus surreptitiously overheard, but none of these have been successful in practice.

. According to our invention we provide that the transmitting and receiving instruments at any two stations shall only be brought into operative connection with one another by the mutual action of the attendants at these two stations, and to this end we provide for breaking, cutting out, or short-circuiting the receivers, as hereinafter described.

In the accompanying drawings, Figure l is a diagrammatic view illustrating one arrangement of our invention and showing the circuit connections between three sets of instruments. Figs. 2, 3, and 4 are views illustrating modifications of our invention. Fig. 5 illustrates a modification of the system which is necessary when a magneto-generator is used for ringing instead of a battery.

Similar letters of reference indicate corre- 5 sponding parts in the several figures, the

same parts in the different sets of instruments shown in stations 2 and 3, Fig. 1, being indicated by the index-figures 2 and 3, respectively.

a is the receiver; b, the hook upon which the same is normally suspended; c, the microphone-transmitter; e, the call-bell; f, the ringing-key; g, the battery; h, the line-wire connecting with switches at other stations; t', the ringing-battery common to several or all of the stations in connection, and j k the lines of the bell-circuit.

Z is the device which we employ for cutting out or short-circuiting the receiver when the apparatus is inoperative.

In the arrangement of our invention shown in Fig. 1 the receiver a is in circuit with the secondary of an induction-coil m, the primary of which is placed in a shunt-circuit n from the main circuit 0, the said secondary or the receiver circuit being out of metallic contact with the primary circuit, the switch, the home line, or earth .or common return. This main circuit 0 contains a relay p, which forms part of the cutting-out device Z, an armature q in connection with which forms part of the sh nut-circuit n and when attracted by the relay closes the said shunt-circuit. With this arrangement it will be understood that so long as the armature q is unattracted-for instance, as sh own at station No. 2-the shuntcircuit at is broken.

Assume now that station No. 1 desires to call station No. 3. The operator moves his selecting-switch r to the contact of line h and operates the ringing-key, with the result that current from the battery 1' flows through the wire it to the ringing-key of station 1, thence through the selecting-switch r and the line h to the telephone -lever b thence through bell e to the linej and back to the battery He then removes his telephone from the hook b, thus breaking the circuit of ringing-battery 1;, and listens for the completion of the speaking-circuit, which produces a clicking sound in the receiver and can only be caused by the cooperation of the station called, (in this case station 3.) Wesometimes combine with the said armature aringing or signaling device, which is operated when the armature is moved. On receiving the call station 3 removes his telephone from the hook and moves his selecting-switch until he hears a click or noise in his receiver caused bycompletion of circuit through speak- Ioo this line, which in the example given will be the line 72 of station No. 1. A current from the local batteries g 9 which are in series, will then flow through the circuit 0, relay 1?, telephone-hook b, line h, selecting-switch r ringing-keyf to battery g and through circuit o relay p telephone-hook 11 line 71, and selecting-switch o back to the battery g, with the result that the armatures g g of the relays p p are attracted to close the shuntcircuits n 97. when a conversation can be carried on without it being possible for station 2 to tap the conversation, as the armature g cannot be attracted until two stations are in a mutual connection, so that the primary of station 2 is in the broken sh untcircuit. When the conversation is finished and the receivers are again hung upon their hooks b 19 the relays p p are demagnetized, so that the shunt-circuits n n are again broken.

In the modification of ourinvention shown in Fig. 3 we arrange for breaking the circuit of the secondary induction-coil containing the receiver by combining with the core of the usual induction-coil an armature s, which normallybreaksthereceiver-circuit. When, however, a call is received by a station, the current which passes through the line and through the primary of the induction-coil at such station and also at the calling-station by the operation of the switches, as above, attracts the armature s and closes the receivercircuit, so that a conversation can be carried on. Then the flow of the currrent through the primary ceases, the circuits of the secondaries are again broken.

In the foregoing arrangements the variations in the current when a conversation is being carried on between two stations will not be sulfieient to energize the core of the induction-coil of any other station and attract the armature and close the receivercircuit of such station.

In the arrangement shown in Fig. 3 we dispense with the induction-coil hereinbefore referred to and substitute therefor an electromagnet 15, having in conjunction with it two armatures u 'LL, which are connected to the line-wire and designed to make contact when attracted by the magnet with contacts 1: o in the receiver-circuit. So long as no direct current is flowing through this magnet the armatures u u are unattracted, so that the receiver is disconnected from the circuit at two points. When, however, current flows through the said magnet, the armatures being attracted make contact with the wires of the receiver, so that a portion of the current flowing through the line-wire then flows through the receiver. It will be understood that with this arrangement the receiver is operated by a direct current instead of by an induced current.

It will be obvious that many modifications may be made without departing from the spirit of this invention. For instance, the breaks in the circuit or circuits may be omitted and in lieu of same the parts of the instrument which it is desired to put out of action, unless a current is passing, may be short-circuited to render the instrument inoperative except when two stations are mutually connected. Such an arrangement is shown in Fig. 4, wherein a short-circuiting device Z is arranged in a short circuit across the circuit of the receiver, the said device 1 normally closing the short circuit and breaking the same when two stations are in mutual connection.

To prevent a third station from being called up by the operation of the ringing-key at a calling-station after the receiver at the called station has been removed from its hook and while the attendant at the latter station is operating his switch or finder key, we arrange the ringing-battery so that the direction of its current is opposed to that of the speaking-battery, thus neutralizing the current of the latter.

Fig. 5 illustrates the method which we employ when a magneto-generator G is used for ringing instead of a battery. In this case we employ a back contact to in connection with the armature q of the relay, which contact is in connection with the common return j, and we employ an extra contact x in connection with the hook I). With this arrangement the operation of the ringing-key fat one station causes a current from the generator to enter the home line of the station to which the switch 7' is connected and thence pass through the bell to the common returnj, as hereinbefore described. It the attendant at the called station removes his receiver from the hook I) while the magneto-current is still passing, the said current flows to the common return through the contacts m and w,

which, with their circuit, constitute a low-re-.

sistance shunt, and is thus prevented from entering the home line of any station to the contact of which the switch 1" is connected.

Having now particularly described and ascertained the nature of our said invention and in what manner the same is to be performed, we declare that what we claim is 1. In an intercom munication system of telephones, the combination with a series of stations, a home line for each station connected with contact-points at other stations and a switch at each station for connecting with said contact-points, of a normally inoperative receiving apparatus at each station and an electrically operated circuit controller at each station for throwing said receiving apparatus out of and into operation, the circuit through said circuit-controller being normally open at the switch of each station whereby said circuit-controllers will not be operated until the switches of the calling and called stations are connected each with the home line of the other station, substantially as described.

2. In anintercommunication system of telephones, the combination with a series of sta- IIO tions, a home line for each station connected with contact-points at other stations and a switch at each station for connecting with said contact-points, of a normallyinoperative receiving apparatus at each station and an electrically operated circuit controller at each station for throwing said receiving apparatus out of and into operation, the circuit through said circuit-controller being normally open at the switch of each station whereby said circuit-controllers will not be operated until the switches of the calling and called stations are connected each with the home line of the other station, a bell-circuit common to all of the stations, a ringing apparatus at each station in the bell-circuit and devices at each station for cutting out the bell-circuit when the telephone of such station is in operation, substantially as described.

3. In an intercommunication system of telephones, the combination with a series of stations, a home line for each station connected with contact-points at other'stations and a switch at each station for connecting with said contact-points, of a normally inoperative receiving apparatus at each station and an electrically operated circuit controller at each station for throwing said receiving apparatus out of and into operation, the circuit through said circuit-controller beingnormally open at the switch of each station, whereby said circuit-controllers will not be operated until the switches of the calling and called stations are connected each with the home line of the other station, a bell-circuit common to all of the stations, a ringing apparatus at each station in the bell-circuit, and devices at each station for cutting out the bell-circuit when the telephone of such station is in operation, a local battery at each station, and a common call-battery in the bell-circuit having the direction of its current opposite to the direction of the current of the local batteries, substantially as. described.

4. In an intercommunication telephone system a series of stations, a home line for each station connected with contacts at the other stations, a switch at each station for connecting with the contacts thereof, a normally inoperative receiving apparatus at each station operated by a normally broken circuit, an electric-circuit controller at each station for closing and opening said normally broken circuit, the circuit through saidcircuit-controller being open at the switch at each station whereby said circuit-controllers will not be operated until the switches of the calling and called stations are each placed in connection with the home line of the other station, substantially as described.

5. In an intercommunication telephone system, a series of stations, a home line for each station connected with contacts at the other stations, a switch at each station for connecting with the contacts thereof, a normally inoperative receiving apparatus at each station located in a secondary circuit, a primary circuit for said secondary circuit, an electric-circuit controller for each station for throwing said receiver into and out of circuit, the circuit through said circuit-controller being open at the said switch at each station whereby the said circuit-controller will not be operated until the switches at the calling and called stations have each been placedin connection with the home line of the other station, substantially as described.

6. In an intercommunication telephone system, a series of stations, a home line for each station connected with contacts at the other stations, a switch at each station for connecting with the contacts thereof a normally inoperative receiving apparatus at each station located in a normally closed secondary G11- cuit, a normally open primary circuit for said secondary circuit, an electric-circuit controling with the contacts thereof, a normally in-' 

